Plant roots need air and water as much as they need nutrients, so, like Goldilocks, they like their beds not too hard and not too soft, not too wet and not too dry. The ideal soil is not only fertile but also friable, i.e., with a fluffy texture affording good aeration and drainage. (It’s been described as resembling devil’s food cake.) When preparing beds in spring, wait until the soil has dried out a bit, and avoid tromping on it as much as you can—compacted soil has less air and water.
Preparing existing beds
Adding compost, well-rotted manure or other organic matter, such as chopped leaves or mushroom compost, is an easy way to improve the texture (or tilth) of existing planting areas, whether your soil is sandy or clayey. Spread a layer of material 4 to 5 centimetres deep over the bed and gently turn it in using a garden fork. If you’re working among existing plants, treat the soil as close to them as possible without damaging their roots. Avoid the tendency to put organic matter only into the individual planting holes. Adding it to the whole area will encourage the roots to spread.
Quick tip: It can be tempting to bash around with a Rototiller, which is quick and easy (and noisy) but, in a word, don’t. Rototilling doesn’t go deep enough, wreaks havoc on the vast population of soil organisms, and ultimately destroys the very soil texture you want to keep.